The present invention relates to an optical device such as a laser diode module used for optical transmissions, and a method for manufacturing the same.
Conventionally, a laser diode module has been used for optical transmissions. The laser diode module is such that a laser diode (LD) element for transmitting light and optical fibers for propagating light from the laser diode element are optically coupled in advance, and these are composed as a module. FIG. 4A and FIG. 4B show one example of a laser diode module in a sectional view.
The laser diode module shown in the same drawings has a metal-made package 9. A laser diode element 1 is disposed and fixed at the fixing portion of a base 10 fixed in the package 9 via a heat sink 11. Also, the tip end side of a lensed fiber 2 having a lens 3 formed at the tip end side of the optical fiber is inserted from an insertion portion 20 secured at the sidewall of the package 9 into the package 9. The tip end side (the attached portion of the lens 3) of the lensed fiber 2 is aligned with the light emitting portion of the laser diode element 1 and is opposed thereto. That is, the laser diode element 1 and lensed fiber 2 are opposed to each other and disposed so that the excitation efficiency (optical coupling efficiency) between the laser diode element 1 and the lensed fiber 2 is maximized.
Also, the package 9 is such that, for example, the bottom plate 22 thereof is made of CuW, and the other portions thereof are made of an Fexe2x80x94Nixe2x80x94Co based alloy represented by KOVAL (Trade name).
The first ferrule 5 is fixed on the base 10 via ferrule retaining portion 16 and 17, and the tip end side of the lensed fiber 2 is inserted into and fixed at the first ferrule 5, and the second ferrule 6 is provided at the rear end side of the first ferrule 5 with a spacing, wherein the intermediate portion of the lensed fiber 2 is inserted into and fixed at the second ferrule 6. The second ferrule 6 is inserted into the insertion portion 20 of the package 9. The second ferrule 6 is fixed at the sidewall of the package 9 via a ferrule fitting portion 15 provided at the package 9.
Metal is plated on the surface of the lensed fiber 2 between the first ferrule 5 and the second ferrule 6. One end side of the metal plated portion 4 is fixed at the second ferrule 6 by soldering 8, and the second ferrule 6 is fixed at the ferrule fitting portion 15 by soldering 7. By the metal plate portion 4 of the lensed fiber 2 being fixed at the second ferrule 6 by soldering and the second ferrule 6 being fixed at the ferrule fitting portion 15 by soldering, the package 9 can be kept hermetic.
The first ferrule 5 is fixed at the ferrule retaining portions 16 and 17 by, for example, YAG laser welding, etc. Also, a monitor photo diode 13 is fixed on the base 10, and a Peltier element module 12 is fixed at the lower side of the base 10. The Peltier module 12 is provided with a Peltier element to keep the temperature of the laser diode element 1 at a fixed level.
As described above, if the laser diode module is constructed by using such a lensed fiber 2, there is an advantage in that the composition of parts can be simplified to reduce production costs. Also, by optimizing the shape of the lens 3 of the lensed fiber 2, the laser diode module having the abovementioned lensed fiber 2 can increase the optical coupling efficiency between the lensed fiber 2 and the laser diode element 2 remarkably. Thus, a laser diode module having very high optical coupling efficiency, which is provided with a lensed fiber 2, is an excellent laser diode module.
Further, in a prior art laser diode module thus constructed, as shown in FIG. 4A, the laser diode module is formed so that no deflection arises in the lensed fiber 2 between the first ferrule 5 and the second ferrule 6 at a temperature (for example, 25xc2x0 C.) for producing the laser diode module.
In order to secure reliability of a laser diode module, at an environmental temperature where the laser diode module is used, it is desirable that no breakage, etc., of the lensed fiber 2 occurs. At present, the temperature at which the laser diode module is used is generally from 0xc2x0 C. through 75xc2x0 C. Also, taking various climatic conditions into consideration, the environmental temperature at which the laser diode module is kept in custody will become xe2x88x9240xc2x0 C. through 85xc2x0 C. Therefore, the environmental temperature at which the laser diode module is used will be from xe2x88x9240xc2x0 C. through 85xc2x0 C. In this temperature range, a laser diode module having no breakage or interruption of the lensed fiber 2 is requested.
However, since a metal-made package 9 has a larger thermal expansion coefficient than a lensed fiber 2 made of a glass-based material, it is liable to expand due to heat. Accordingly, as the environmental temperature for use rises, the distance between the first ferrule 5 and the second ferrule 6 varies and increases. And, as the environmental temperature where the laser diode module is used becomes higher than the production temperature, the distance between the first ferrule 5 and the second ferrule 6 becomes large as shown in FIG. 4B. On the other hand, the thermal expansion coefficient of the lensed fiber 2 is very slight in comparison with that of the package 9, and it hardly changes due to changes in the abovementioned environmental temperature for use. Therefore, a tensile stress is applied to the lensed fiber 2 fixed between the first ferrule 5 and the second ferrule 6.
Further, as described above, since an optical fiber such as a lensed fiber 2 is made of a glass-based material, and is very weak to tensile stress, in prior art laser diode modules, a problem such as breakage arises in the lensed fiber 2 due to a tensile stress applied onto the lensed fiber 2 in high temperatures. Further, instead of breakage of the lensed fiber 2, such trouble occurs, in which the lensed fiber 2 is separated from the first ferrule 5 or the second ferrule 6 at the fixing portion. Such breakage of the lensed fiber 2 or the problem of separation at the fixing portion may damage the reliability of a laser diode module, and these were critical problems.
The present invention was developed in order to solve such problems in the prior arts, and it is therefore an object of the invention to provide an optical device such as a laser diode module, having high reliability, in which no break occurs in an optical fiber at an environmental temperature for use, and optical fibers are not separated from the ferrules at the fixing portion, and a method for producing the same.
In order to achieve the abovementioned object, the present invention employs the following construction as the means for solving the problems. That is, an optical device according to the first aspect of the invention is featured in that the first ferrule in which an optical fiber is inserted and fixed is fixed in a package formed of a material having a larger thermal expansion coefficient than that of the optical fiber, the second ferrule in which the optical fiber is inserted and fixed is fixed in the package at a position spaced from the first ferrule in the lengthwise direction of the optical fiber, and the distance between the first ferrule and the second ferrule varies and increases as the environmental temperature for use of the optical device rises, wherein the optical device is provided with a tensile stress suppressing means which can prevent a tensile stress exceeding a specified allowable range from being applied to an optical fiber between the first ferrule and the second ferrule at the upper limit of the environmental temperature for use.
An optical device according to the second aspect of the invention is featured in that, in addition to the first aspect, a means for preventing the above tensile stress from being applied is based on a deflection formed in an optical fiber between the first ferrule and the second ferrule at a lower temperature than the upper limit of the environmental temperature for use.
Further, an optical device according to the third aspect of the invention is featured in that, in addition to the first aspect, a laser diode element is disposed and fixed at the fixing portion of the base fixed at the tip end side of an optical fiber, the tip end side of a lensed fiber on which a lens is formed at the tip end side of the optical fiber is inserted into a package through an insertion portion secured at the side wall of the package, the tip end side of the corresponding lensed fiber is aligned with a limit emitting portion of the laser diode element and is opposed thereto, the tip end side of the lensed fiber is inserted into and fixed in the first ferrule with the first ferrule fixed on the base, the second ferrule is secured at the rear end side of the corresponding first ferrule via a spacing, an intermediate portion of the lensed fiber is inserted into and fixed at the second ferrule, and the corresponding second ferrule is inserted into the insertion portion of the package and is fixed at the side wall of the package.
In addition, an optical device according to the fourth aspect of the invention is featured in that, in addition to the second aspect, a laser diode element is disposed and fixed at the fixing portion of the base fixed in the package, the tip end side of the lensed fiber in which a lens is formed at the tip end side of an optical fiber is inserted into a package through an insertion portion secured at the side wall of the package, the tip end side of the corresponding lensed fiber is aligned with the light emitting portion of the laser diode element and is opposed thereto, the tip end side of the lensed fiber is inserted into and fixed in the corresponding first ferrule with the first ferrule fixed on the base, the second ferrule is provided at the rear end side of the corresponding first ferrule via a spacing, an intermediate portion of the lensed fiber is inserted into and fixed at the corresponding second ferrule, and the corresponding second ferrule is inserted into the insertion portion of the package and is fixed at the sidewall of the package.
Still further, an optical device according to the fifth aspect of the invention is featured in that, in addition to the fourth aspect, the distance between the first ferrule and the second ferrule is set to 7.5 mm through 30 mm at 25xc2x0 C., and an amount of deflection of a lensed fiber between the first ferrule and the second ferrule at 25xc2x0 C. is set to 3 xcexcm through 15 xcexcm.
Further, a method for producing an optical device according to the sixth aspect of the invention is a method for producing an optical device constructed according to the third, fourth or fifth aspect of the invention and is featured in that, after the tip end side of a lensed fiber is inserted into and fixed at the first ferrule and fixed on a base, the second ferrule in which any intermediate portion of the lensed fiber is fixed is secured in a package so that no deflection is formed on the lensed fiber between the first ferrule and the second ferrule under a temperature condition defined in advance around the upper limit of the environmental temperature for use.
Furthermore, a method for producing an optical device according to the seventh aspect of the invention is featured in that, in addition to the sixth aspect, the temperature at which the second ferrule is fixed in a package is set to 80xc2x0 C. through 110xc2x0 C.
Still further, a method for producing an optical device according to the eighth aspect of the invention is a method for producing an optical device constructed according to the third, fourth, or fifth aspect, and is featured in that the second ferrule fixing temperature which is lower than the upper limit of the environmental temperature for use is determined, and an amount of deflection of an optical fiber is obtained at the second ferrule fixing temperature which can suppress or prevent a tensile stress exceeding the allowable range from being applied to the lensed fiber between the first and second ferrules at the upper limit of the environmental temperature for use, wherein after the tip end side of the lensed fiber is inserted into and fixed at the first ferrule and is fixed on the base, a deflection equivalent to the amount of deflection is formed on the lensed fiber between the first ferrule and the second ferrule under the second ferrule fixing temperature conditions, and in this state the second ferrule in which any intermediate portion of the lensed fiber is fixed is secured in the package.
In an optical device constructed in respective constructions of the invention, the first ferrule in which an optical fiber is inserted and fixed and the second ferrule in which an optical ferrule is inserted and fixed have a spacing in the lengthwise direction of the optical fiber. And, as the environmental temperature for use of an optical device is increased, the distance between the first ferrule and the second ferrule varies and increases. However, an optical device according to the invention is provided with a means for preventing a tensile stress exceeding the allowable range from being applied onto an optical fiber between the first ferrule and the second ferrule at the upper limit of the environmental temperature for use. Therefore, the optical device according to the invention can prevent a tensile stress exceeding the allowable range from being applied onto an optical fiber between the first ferrule and the second ferrule.
Accordingly, an optical device according to the invention can prevent an optical fiber between the first ferrule and the second ferrule from being broken or interrupted, and prevent the fixing portion between the optical fiber and the first or the second ferrule from being disconnected.
Also, the means for preventing a tensile stress from being applied can be easily formed by a deflection formed in an optical fiber between the first ferrule and the second ferrule at, for example, a lower temperature than the upper limit of the environmental temperature for use. Also, since a stress due to the deflection is further dispersed to the entirety of an optical fiber in comparison with a tensile stress, stress can be prevented from becoming concentrated at a specified place such as a fixing portion of an optical fiber in a ferrule. Accordingly, in an optical device according to the second aspect of the invention, in which the deflection is utilized as a means for preventing a tensile stress from being applied, there is no case where an optical fiber is broken due to the deflection and the optical fiber is disconnected from the ferrules.
Also, an optical device according to the second aspect of the invention, in which the deflection is utilized as the means for preventing a tensile stress from being applied, can simply prevent a tensile stress from being applied onto an optical fiber by using a very simple means, which is the deflection of the optical fiber, as the means for preventing a tensile stress from being applied. Also, in this construction, since it is very simple to change the amount of deflection of an optical fiber, it is possible to instantaneously deal with changes in design of packages.
Further, an optical device according to the third and fourth aspects of the invention is such that a laser diode element fixed at the fixing portion of the base fixed in a package is optically coupled with a lensed fiber, and the lensed fiber is inserted into and fixed at the first ferrule and the second ferrule via a spacing in the lengthwise direction of the optical fiber. By an optical device according to the third aspect and the fourth aspect of the invention, an optical device thus constructed can be made into an excellent optical fiber which brings about the excellent effects described above.
In addition, according to an optical device of the fifth aspect of the invention, in compliance with the specifications of the optical device according to the fourth aspect, it becomes possible to accurately control the distance between the first ferrule and the second ferrule, and the amount of deflection at 25xc2x0 C. Therefore, the fifth aspect of the invention can securely prevent a tensile force exceeding the allowable range from being applied onto an optical fiber between the first ferrule and the second ferrule in an optical device such as a laser diode module in which the upper limit of the environmental temperature for use is approximately 85xc2x0 C.
Further, with a method for producing an optical device according to each of the constructions of the invention, the amount of deflection of an lensed fiber between the first ferrule and the second ferrule can be accurately controlled, whereby it is possible to produce an optical device which can bring about the abovementioned excellent effects.